Reportedly, changes to Google’s search algorithms will be effective April 21st as it intends to increase the ranking of sites that are optimized for mobile use.
They’ve said it will have a “significant impact” on mobile searches across all languages and the world but users will receive more quality search results.
A company spokesman said, "These changes are great news for mobile users as it should help motivate those sites that still don’t have a mobile site to actually build one. Google started highlighting mobile-friendly sites in results last year."
Any site admins who wish to test their mobile compatibility may use Google’s evaluation tools available here.